(Z)-2-cyano-3-hydroxy-but-2-enoic acid-(4′-trifluoromethylphenyl)-amide (Teriflunomide) has the structure illustrated in Formula I:

(Z)-2-cyano-3-hydroxy-but-2-enoic acid-(4′-trifluoromethylphenyl)-amide (Teriflunomide, Formula I) use in treating chronic graft-versus-host disease has been disclosed in U.S. Pat. No. 4,965,276 issued on Oct. 23, 1990. U.S. Pat. No. 5,459,163 issued on Oct. 21, 1997 and U.S. Pat. No. 5,679,709 issued on Oct. 21, 1997 disclose compositions useful for treating autoimmune diseases in particular lupus erythematosus. Teriflunomide has been shown to produce antiproliferative effects on a wide variety of immune cells and cell lines (Cherwinski H. M., et al., J. Pharmacol. Exp. Ther. 1995; 272:460-8; Prkash A., et al., Drugs 1999; 58(6):1137-66; Bartlett R. R. et al., Agent Action 1991; 32(1-2):10-21). Additionally, it inhibits the enzyme dihydroorotate dehydrogenase, an enzyme essential for the synthesis of pyrimidines (Bruneau J-M, et al., Biochem. J. 1998; 36:299-303). European Patent 1381356 B1 discloses the use of Teriflunomide for the manufacture of a medicament for treating multiple sclerosis wherein said medicament is administered orally. International Application WO 2007/118684 discloses Leflunomide containing solid pharmaceutical compositions including an organic or inorganic acid characterized by improved stability. Said compositions show a slighter decomposition of Leflunomide to Teriflunomide than in commercial Arava® tablets. Teriflunomide amounts are disclosed which range from 0.02 mg to 0.511 mg per tablet containing 10 mg of Leflunomide. These are less than 0.35% Teriflunomide with respect to the total mass of the tablet, which is 150 mg.
A solid pharmaceutical formulation for Teriflunomide was developed for use in clinical studies. One of the observations made during stability studies was a strong increase in one degradant, which is 2-cyano-N-(4-trifluoromethyl-phenyl)-acetamide and has the structure illustrated in Formula II:

At room temperature storage 2-cyano-N-(4-trifluoromethyl-phenyl)-acetamide levels of up to 0.2% are reached in the solid pharmaceutical formulation after 12 month storage [Teriflunomide 7 mg tablets, Al/PVC blisters, storage at 25±2° C. and 60% relative humidity {RH}]. A further degradant could be 4-trifluoromethyl-aniline.
It is an object of the present invention to find a solid pharmaceutical formulation for Teriflunomide which does not have the disadvantages of increased concentrations of 2-cyano-N-(4-trifluoromethyl-phenyl)-acetamide or 4-trifluoromethyl-aniline (4-TFMA).
It has been found that some solid pharmaceutical formulations for Teriflunomide without colloidal silicon dioxide do not have the disadvantages mentioned which is limited increase in 2-cyano-N-(4-trifluoromethyl-phenyl)-acetamide formation and limited formation of 4-TFMA
It has further been found advantageous to add an acidic reacting compound to said solid pharmaceutical formulation for Teriflunomide without colloidal silicon dioxide.
It has also been additionally found advantageous to add an acid reacting compound to solid formulations of Teriflunomide containing colloidal silicon dioxide.